SUMMARY
Dolphin crashed after creating a new folder in an sftp folder. I haven't been able to reproduce the crash again.

WHAT I WAS DOING BEFORE THE CRASH
1. In an sftp folder, press F10
2. Type a folder name in the window that appears
3. Press 'enter'

OBSERVED RESULT
Dolphin crashed. On opening the folder again, I saw that the folder I was attempting to create indeed got successfully created.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.24.1
KDE Frameworks Version: 5.91.0
Qt Version: 5.15.2
Kernel Version: 5.16.10-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 4 × Unknown Type, 4 × AMD Ryzen 5 3500U with Radeon Vega Mobile Gfx
Memory: 21.5 GiB of RAM
Graphics Processor: AMD Radeon Vega 8 Graphics

ADDITIONAL INFORMATION
I had created a few new folders just before this crash without triggering any crash. I haven't observed this crash again, so I am probably missing something in the reproduction steps.

BACKTRACE
Application: டால்பின் (dolphin), signal: Segmentation fault
Content of s_kcrashErrorMessage: {_M_t = {<std::__uniq_ptr_impl<char, std::default_delete<char []> >> = {_M_t = std::tuple containing = {[1] = 0x0, [2] = {<No data fields>}}}, <No data fields>}}
[KCrash Handler]
#6  0x00007f1d1c36e576 in QLineEdit::text() const () from /usr/lib/libQt5Widgets.so.5
#7  0x00007f1d1d542899 in KNewFileMenuPrivate::_k_slotStatResult (job=0x7f1d0805f530, this=0x55cdd2ce2f40) at /usr/src/debug/kio-5.91.0/src/filewidgets/knewfilemenu.cpp:1229
#8  operator() (job=0x7f1d0805f530, __closure=<optimized out>) at /usr/src/debug/kio-5.91.0/src/filewidgets/knewfilemenu.cpp:1210
#9  QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<KJob*>, void, KNewFileMenuPrivate::_k_slotTextChanged(const QString&)::<lambda(KJob*)> >::call (arg=<optimized out>, f=...) at /usr/include/qt/QtCore/qobjectdefs_impl.h:146
#10 QtPrivate::Functor<KNewFileMenuPrivate::_k_slotTextChanged(const QString&)::<lambda(KJob*)>, 1>::call<QtPrivate::List<KJob*>, void> (arg=<optimized out>, f=...) at /usr/include/qt/QtCore/qobjectdefs_impl.h:256
#11 QtPrivate::QFunctorSlotObject<KNewFileMenuPrivate::_k_slotTextChanged(const QString&)::<lambda(KJob*)>, 1, QtPrivate::List<KJob*>, void>::impl (which=<optimized out>, r=<optimized out>, ret=<optimized out>, a=<optimized out>, this_=<optimized out>) at /usr/include/qt/QtCore/qobjectdefs_impl.h:443
#12 QtPrivate::QFunctorSlotObject<KNewFileMenuPrivate::_k_slotTextChanged(const QString&)::<lambda(KJob*)>, 1, QtPrivate::List<KJob*>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void **, bool *) (which=<optimized out>, this_=<optimized out>, r=<optimized out>, a=<optimized out>, ret=<optimized out>) at /usr/include/qt/QtCore/qobjectdefs_impl.h:436
#13 0x00007f1d1b7ef9d3 in QtPrivate::QSlotObjectBase::call (a=<optimized out>, r=<optimized out>, this=<optimized out>, this=<optimized out>, r=<optimized out>, a=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#14 doActivate<false> (sender=0x7f1d0805f530, signal_index=6, argv=0x7ffd6e979df0) at kernel/qobject.cpp:3886
#15 0x00007f1d1c9403b1 in KJob::result (this=this@entry=0x7f1d0805f530, _t1=<optimized out>, _t1@entry=0x7f1d0805f530, _t2=...) at /usr/src/debug/build/src/lib/KF5CoreAddons_autogen/include/moc_kjob.cpp:633
#16 0x00007f1d1c94482c in KJob::finishJob (this=0x7f1d0805f530, emitResult=<optimized out>) at /usr/src/debug/kcoreaddons-5.91.0/src/lib/jobs/kjob.cpp:98
#17 0x00007f1d1b7ef9d3 in QtPrivate::QSlotObjectBase::call (a=<optimized out>, r=<optimized out>, this=<optimized out>, this=<optimized out>, r=<optimized out>, a=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#18 doActivate<false> (sender=0x55cdd447eed0, signal_index=7, argv=0x7ffd6e979ec0) at kernel/qobject.cpp:3886
#19 0x00007f1d1d0ce847 in KIO::SlaveInterface::dispatch (this=0x55cdd447eed0, _cmd=104, rawdata=...) at /usr/src/debug/kio-5.91.0/src/core/slaveinterface.cpp:149
#20 0x00007f1d1d0c79dd in KIO::SlaveInterface::dispatch (this=0x55cdd447eed0) at /usr/src/debug/kio-5.91.0/src/core/slaveinterface.cpp:78
#21 0x00007f1d1d0cb3d3 in KIO::Slave::gotInput (this=0x55cdd447eed0) at /usr/src/debug/kio-5.91.0/src/core/slave.cpp:336
#22 0x00007f1d1b7ef9d3 in QtPrivate::QSlotObjectBase::call (a=<optimized out>, r=<optimized out>, this=<optimized out>, this=<optimized out>, r=<optimized out>, a=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#23 doActivate<false> (sender=0x55cdd4203d00, signal_index=3, argv=0x7ffd6e97a100) at kernel/qobject.cpp:3886
#24 0x00007f1d1b7e2dc6 in QObject::event (this=<optimized out>, e=0x55cdd4630760) at kernel/qobject.cpp:1314
#25 0x00007f1d1c2351a6 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#26 0x00007f1d1b7beb9a in QCoreApplication::notifyInternal2 (receiver=0x55cdd4203d00, event=0x55cdd4630760) at kernel/qcoreapplication.cpp:1064
#27 0x00007f1d1b7bf699 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x55cdd29a6d50) at kernel/qcoreapplication.cpp:1821
#28 0x00007f1d1b806bd8 in postEventSourceDispatch (s=0x55cdd2a7ac30) at kernel/qeventdispatcher_glib.cpp:277
#29 0x00007f1d194a7f13 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#30 0x00007f1d194fe0d9 in ?? () from /usr/lib/libglib-2.0.so.0
#31 0x00007f1d194a5485 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#32 0x00007f1d1b80aada in QEventDispatcherGlib::processEvents (this=0x55cdd2a84a60, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#33 0x00007f1d1b7b6e6b in QEventLoop::exec (this=0x7ffd6e97a590, flags=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#34 0x00007f1d1b7c25c7 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#35 0x000055cdd24621b1 in main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/dolphin-21.12.2.1/src/main.cpp:230
[Inferior 1 (process 229839) detached]